I've found my external tank to be extremely useful and has turned some of my otherwise useless-in-a-war weapons into potent and functional arms. For those unfamiliar with the parts involved in making your own low pressure air tank I've made a simple write-up.
The numbered list items under each header correlate with the numbered items in this diagram.

A NOTE ON TANK SAFETY
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1. With a standing bike pump you're not going to be able to fill the tank any higher than 65psi, so you'll be safe in that regard since the maximum rated pressure of the PVC pipe is 120psi. A handheld pump won't be able to go above 40 psi.
2. If you want to be able to fill the tank with a compressor YOU MUST HAVE a pressure gauge on the tank, a regulator to step down the output pressure level, and you SHOULD NEVER attempt to fill any kind of PVC pipe to it's maximum pressure rating.
3. For this type of tank it's best not to fill beyond 100psi. If you want a higher capacity tank, purchase a purpose-made tank with a higher rating.
4. I have a pressure gauge on my tank so that I can monitor tank capacity and to make sure it doesn't have a leak. It can be added anywhere you want it, but I recommend putting it on the tank side of the check valve so you can watch the gauge while you're filling. It also allows you to monitor how much air volume is expended each time any given gun is fired. Certain guns expend more air than others.

Construction
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1. Cut 3" PVC Pipe to desired length (anywhere from 12" to 20" depending on how big of a tank you can fit on your back)
2. Use PVC Primer on end of the 3" PVC pipe section and the 3" PVC pipe caps. Pre both with PVC cement and then joint them together using a wood blank and hammer.
3. Use the same process to glue the 3" PVC cap into one pipe coupler
4. And to glue the 3" Reducing Hex Bushing into the other pipe coupler
5. Apply some epoxy sealant on the thread of the threaded 1"-to-1/4"Hex Reduce Bushing and screw it into the 3" Reducing hex bushing.
6. Apply some epoxy sealant on the Instant Tube fitting and screw it into the 1"-to-1/4" Hex Reduce Bushing.
7. Use a box cutter or X-acto knife to cut a short length of Polyethylene tubing and insert it into the Instant tube fitting.
8. Attach the Tee fitting onto the other end of the tubing.
9. Cut two lengths of PVC tubing that will easily reach from the Tee to about your waist when the tank is mounted on your back.
10. Install the Check Valve Coupler onto the end of one of the lengths of tubing. Make sure the arrow points to the tank so that it will allow the pump to fill the tank, but not allow the tank to empty once the pump is disconnected.
11. Install the Tube x Stem adapter onto the pump fitting. Then cut a roughly two foot long length of PVC or polyethylene tubing to connect the Tube x Stem adapter to the Check Valve Coupler.
12. Connect the Instant Tube Coupler to the other line.
13. This line will connect to the gun(s) you plan to use the tank with, and how you accomplish that is highly dependent upon the dimensions of the tubing in the gun itself. Some guns have metric dimension tubing, others have imperial dimension tubing, but with strange inner diameters. The magstrike specifically has 1/4" OD tubing that can plug directly into this type of coupler.

And to use either gun without the tank you will simply need a stem plug to put in the fitting where you would normally connect the tank.
51025K254 - Nylon Plug, 1/4" OD = $0.63

14. If you later plan to fill the tank beyond 65psi, or you would like to control the pressure level the gun receives, you will need a non-relieving type regulator to reduce the output pressure to a safe level that won't damage the internals of your gun.
Only a non-relieving type of regulator is meant to be used with a tank supply. Most regulators are designed to be used with compressors and will regulate their output by exhausting the overpressure to the atmosphere. In other words they will constantly "leak" and empty your tank in no time.
A regulator will also in turn will help to conserve the capacity of your tank when the gun is in use since you can set it to only deliver the amount of pressure needed to effective fire the gun.

And finally, here's a ready made set of materials available through Mcmaster that will allow you to make your own tank. Only some of these items are available through any given hardware store. Buying anything except the 3" PVC pipe locally will most definitely end up costing more.

Nice CaptainSlug. But, don't the endcaps fit over the PVC, just like a coupler? I don't know about larger sizes, but with smaller sizes (<1-1/4") they all fit over top, so they have almost the same ID as the PVC's OD.

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QUOTE(VACC @ Jan 24 2008, 06:12 AM)

I am NEVER going to sleep naked in the bed of a former child star ever again....seriously

Nice CaptainSlug. But, don't the endcaps fit over the PVC, just like a coupler? I don't know about larger sizes, but with smaller sizes (<1-1/4") they all fit over top, so they have almost the same ID as the PVC's OD.

You would think so, but no. Sizes 3/4" and larger are inserted into a coupler to seal a pipe end.If you want to see for yourself go to the plumbing department of the hardware store.

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

Wow, that is really weird, because I found a few stores that have standard PVC fittings, and even for 1" the fit over the PVC pipe. Might be a different type of fitting, possibly pressure rated?

It depends on the size you're talking about. Pipe caps and Pipe END caps can be easily confused with each other but are not interchangeable. END caps are not ideal for making a tank because they tend to be thin wall.

If you buy a 3" PIPE CAP and 3" PVC pipe the two will have the same outer diameter, and therefore the 3" PIPE CAP will not fit over the end.Certain pipe caps of a size larger than the pipe you are trying to plug will fit onto that pipe size. Since there are fewer size intervals in larger pipe sizes, you don't really have that option.

Larger sizes of pipe are in intervals further apart, and would make that not possible. I used 3" SCH40 PVC pipe to make my tank and there are NO PIPE CAPS that slip over the end of that size of pipe. I looked at Home Depot, Lowes, and ordered from Mcmaster and got the same thing. Caps with an outer diameter the same as the pipe itself.

Edited by CaptainSlug, 05 April 2007 - 12:46 AM.

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

I'm probably going to build one of these eventually but do you know what I need to hook this up to a titan and also is it possible to interchange the guns so one day I could use a titan and the next day I could use a magstrike? Also great job on making this.

I'm probably going to build one of these eventually but do you know what I need to hook this up to a titan and also is it possible to interchange the guns so one day I could use a titan and the next day I could use a magstrike? Also great job on making this.

Thanks to the instant tube fittings you don't need any other special parts to switch which gun is connected to the tank. You simply push the outer ring of the fitting then pull the tubing out.

However the Titan will drain the tank after only 10 shots because it uses such a high volume of air.

You can either drill a small hole on the back of the blast chamber then install an instant tube fitting there, or you can install one as a replacement for the stock pump. There's not alot of tubing inside the gun to work with for adding fittings because the blast chamber is hooked up to the pump output directly.

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

Supposing I have a pipe cap that fits over 2" and that is what I am making my tank out of, could you explain what I should do? They are curved a bit on the top. The guy at the store said they just started stocking the caps for this size.

Yeah, it would be nice if you could explain that.

-Sharpie

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"If only you could upgrade to a bigger one. Double the length and watch as others cower in fear of your balls." -Shadow Hunter Alpha

"I had just used some silicone spray on the plunger, and saw a nice increase in range. So I told my wife that lubing up makes my balls shoot further." -Carbon

End Caps like what you're describing are not pressure rated, but should be able to withstand pressure levels under 80PSI. You have to adhere it to the end of the pipe using PVC primer and then PVC cement.

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

1. Too low for what? If that's the maximum pressure rating on the parts you are buying then they're useless for making a tank.If 45 PSI is the maximum pressure output of the pump you're using it will be fine. Even the strongest manual bike pumps can't output beyond 65psi.A regulator is only vital if you;re trying to fill the tank beyond the pressure level that's safe for the internals of the gun you're hooking up to it. Most Nerf guns are capable of functioning at a maximum pressure level of 70psi.2. Yes

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

How would I go about making a type of "backpack" tank? I was thinking, so could I connect it to mutiple air guns, then put some type of valve to control airflow so I don't waste all the air in one shot? Thanks, El- Cheapo

1. How would I go about making a type of "backpack" tank? 2. I was thinking, so could I connect it to mutiple air guns, then put some type of valve to control airflow so I don't waste all the air in one shot? Thanks, El- Cheapo

1. It's all in the first post.2. That depends on what kind of valve system is in the gun. The Blastfire and Hornet both have a valve system that prevents the supply from continually emptying under a long trigger pull. However the Airtech and Supermaxx lines as well as the Titan have a simply dump valve which is linked directly to the trigger. Those would need a regular ball valve inbetween the blast chamber of the gun and the backpack tank and you would have to toggle it on-off inbetween shots to fill the blast chamber, then to close it off from the tank so that the tank doesn't continue emptying when the trigger is held down.

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

1. How would I go about making a type of "backpack" tank? 2. I was thinking, so could I connect it to mutiple air guns, then put some type of valve to control airflow so I don't waste all the air in one shot? Thanks, El- Cheapo

1. It's all in the first post.2. That depends on what kind of valve system is in the gun. The Blastfire and Hornet both have a valve system that prevents the supply from continually emptying under a long trigger pull. However the Airtech and Supermaxx lines as well as the Titan have a simply dump valve which is linked directly to the trigger. Those would need a regular ball valve inbetween the blast chamber of the gun and the backpack tank and you would have to toggle it on-off inbetween shots to fill the blast chamber, then to close it off from the tank so that the tank doesn't continue emptying when the trigger is held down.

So, let's say an AT3K would use all the air if you just held the trigger? Also, an air regulator for air tools would work for this, wouldn't it? I wasn't sure as to which to type of regulator you were referring to the name confused me somewhat).

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QUOTE(VACC @ Jan 24 2008, 06:12 AM)

I am NEVER going to sleep naked in the bed of a former child star ever again....seriously

1. So, let's say an AT3K would use all the air if you just held the trigger? 2. Also, an air regulator for air tools would work for this, wouldn't it? I wasn't sure as to which to type of regulator you were referring to the name confused me somewhat).

1. Correct. It has a dump valve which will remain open as long as you hold the trigger down. It's also dependent upon the speed at which you pull the trigger.2. Air regulators for air tools are relieving type. That means they will exhaust to atmosphere excess pressure to regulate the output. This is the type of regulator you DO NOT WANT TO USE for obvious reasons. Non-relieving regulators have spring loaded piston set to a tension that closes the valve off from the input at a certain pressure level. This regulates the output without wasting any air.See: http://www.docsmachi...m/tech/fig1.jpg

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

So if I want to shoot further, all I have to do is dial up the regulator? And if I'm using an Airtech, I just have to pull the trigger longer? I have another question. What if I put a regulator at the back of the air tank on a titan. Will the tank stop filling after it reaches a certain PSI, is that how regulators work?

1. So if I want to shoot further, all I have to do is dial up the regulator? 2. And if I'm using an Airtech, I just have to pull the trigger longer? 3. I have another question. What if I put a regulator at the back of the air tank on a titan. Will the tank stop filling after it reaches a certain PSI, is that how regulators work?

1. Sort of. Any given gun has an optimal operating pressure ranges. A maximum effective operating pressure level, and a minimum. The maximum is determined by how air-tight the mechanism is, the pressure level the mechanism can withstand, and the length of the barrel.2. There's not point in holding the trigger down longer considering the dart as already left the barrel.3. Correct. The Titan and the Airtechs don't actually need a high pressure level to be effective and a regulator is a very effective way to limit the pressure output level of a tank to both conserve the tank, and to improve the consistency of the gun's performance.

However due to its high volume blast chamber the downside of using a Titan with a backpack tank exactly like mine is that one tank fill is only going to give you 10-15 shots even when regulated. Adding a ball valve before the tank input on the Titan might improve that a bit though.

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The little critters of nature, they don't know that they're ugly. That's very funny, a fly marrying a bumble bee. I told you I'd shoot, but you didn't believe me. Why didn't you believe me?

In order to convert this to a bladder-type tank, would I need to do anything besides affix a durable rubber membrane to the end of the size adapter bushing and drill some holes in the bottom of the tank (to relieve the pressure built up when the outside of the bladder expands and compresses the air within the PVC shell of the tank)? Or would this not work the way I would want/expect it to.

Edited by SHADOW HUNTER ALPHA, 08 May 2007 - 09:33 PM.

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The only commonly shared fate among us all is death. I turn to the shadows so that I may not be unfamiliar with hell's corridors when I arrive. - SHADOW HUNTER ALPHA

Founder of the Shadow Militia.Founder of Nightshade Laboratories and The Nightshade Armament Corporation.

Building a bladder style tank is very difficult and I doubt that it will offer more shot capacity than this already very large rigid tank.

It wasn't the capacity I was trying to improve, it was maintaining a constant or near-constant pressure level for a longer time. (I may be working on a special project to keep me busy until summer comes and I can get to work on my shotty [Piney, it's only one more month until I can finally do something]).

Edited by SHADOW HUNTER ALPHA, 08 May 2007 - 09:54 PM.

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The only commonly shared fate among us all is death. I turn to the shadows so that I may not be unfamiliar with hell's corridors when I arrive. - SHADOW HUNTER ALPHA

Founder of the Shadow Militia.Founder of Nightshade Laboratories and The Nightshade Armament Corporation.

A NOTE ON TANK SAFETY----------------------------------------1. With a standing bike pump you're not going to be able to fill the tank any higher than 65psi, so you'll be safe in that regard since the maximum rated pressure of the PVC pipe is 120psi. A handheld pump won't be able to go above 40 psi.2. If you want to be able to fill the tank with a compressor YOU MUST HAVE a pressure gauge on the tank, a regulator to step down the output pressure level, and you SHOULD NEVER attempt to fill any kind of PVC pipe to it's maximum pressure rating. 3. For this type of tank it's best not to fill beyond 100psi. If you want a higher capacity tank, purchase a purpose-made tank with a higher rating.4. I have a pressure gauge on my tank so that I can monitor tank capacity and to make sure it doesn't have a leak. It can be added anywhere you want it, but I recommend putting it on the tank side of the check valve so you can watch the gauge while you're filling. It also allows you to monitor how much air volume is expended each time any given gun is fired. Certain guns expend more air than others.

Cool tank and also nice with the safety tip.

I was testing my air powered potato launcher, and I stupidly let the glue dry only 2 hours (the can said 1 hour). So I pump it up to only 30 PSI, and there is a big WHUMP, and the end cap shoots off, almost hits my leg, and rips my pump in half. We found the end cap/half of pump in a tree later.